1. Field of the Invention
The present invention relates to a toner for electrostatic-image development, which is used for image formation of an electrophotographic method.
2. Description of the Related Art
In recent years, in order to further save energy in the image forming device of an electrophotographic method, there has been required a toner for electrostatic-image development (which hereinafter may be simply referred to as a “toner”) with which heat fixing can be performed at a lower temperature. In such a toner, in order to achieve more excellent low-temperature fixing property and stably form a high quality image over a long period of time, there has been required a toner that satisfies long-term stability of charging.
As a toner having low-temperature fixing property, for example, there is proposed a toner to which low-temperature plasticity and flexibility are imparted through the use of, as a binder resin, a copolymer of a macromonomer obtained by binding, to a vinyl monomer, an oligomer of a resin having a low glass-transition temperature or a low melting point (for example, see Patent Literature 1).
In addition, for example, there is widely known a toner that contains a crystalline material as a fixing aid, specifically, a crystalline ester compound such as a crystalline polyester resin or a fatty acid ester compound (for example, see Patent Literature 2).
However, with the toner as disclosed in Patent Literature 1, it has not been possible to satisfactorily obtain both low-temperature fixing property and heat-resistant storability.
Moreover, in the toner containing the fixing aid as disclosed in Patent Literature 2, there exists a problem in which it is not possible to obtain a sufficient strength of a fixed image formed due to a low compatibility between a crystalline ester compound and a binder resin at the time of heat fixing or a problem of a low long-term stability of charging such as the change in the quality of the image formed when an image is formed over a long period of time.
In order to solve such problems, it is proposed that by the control of the compatibility between a binder resin and a crystalline ester compound, the crystalline ester compound is caused to exist in a crystallized state in toner particles, and the crystalline ester compound and the binder resin are made compatible with each other at the time of heat fixing, with the result that both low-temperature fixing property and long-term stability of charging are obtained (see Patent Literatures 3 and 4).
However, in fact, with the toner as described above, it is not possible to sufficiently satisfy the requests for low-temperature fixing property and long-term stability of charging, which are being increasingly made.